Wastewater concentration method

ABSTRACT

There are disclosed herein equipment and methods for screening and concentrating wastewater overflow from combined sewer systems. Exemplary equipment includes a separator employing a substantially cylindrical rotating screen. Influent is piped upwardly into the equipment and deflected outwardly toward the inner surface of the screen in a manner to achieve a desired flow rate and flow pattern of the influent onto the screen. Means are provided for controlling the flow rate and for suitably directing the influent in a plurality of substantially discrete inclined streams toward the inner surface of the rotating screen. The screen is rotated at a speed to achieve a desired centrifugal force. Effluent passes through the screen to an outlet and the remaining concentrate passes to an outlet. A certain amount of the influent splashes from the inner surface of the screen, and is received by a backsplash pan and may be recirculated and rescreened. The screen is in the form of a screen cage having a plurality of removable screen panels for facilitating replacement of damaged screens or changing of screen type or mesh size. Cleaning means is provided for directing a cleaning fluid periodically at the screen. The methods disclosed involve the manner in which the influent, effluent, concentrate and backsplash are handled, and the manner in which the influent is screened to achieve a fluid concentrate which is pumpable to other treatment equipment for ultimate disposal. Additionally, a sequence of influent feed and screen cleaning is described.

United States Patent n 1 3,627,130

[72] Inventors Walter J. TalleyJr- ABSTRACT: There are disclosed hereinequipment and Brentwood Park; methods for screening and concentratingwastewater overflow Howard W. Wright, Jr., San Gabriel, b th fromcombined sewer systems. Exemplary equipment includes of Calif. aseparator employing a substantially cylindrical rotating [21] App]. No.42,100 screen. lnfluent is piped upwardly into the equipment and [22]Filed June 1, 1970 deflected outwardly toward the inner surface of thescreen in a [45] Patented Dec. 14, 1971 manner to achieve a desired flowrate and flow pattern of the [73] Assignee Sweco, lnc. influent onto thescreen. Means are provided for controlling Los Angeles, Calif. the flowrate and for suitably directing the influent in a plurality ofsubstantially discrete inclined streams toward the inner surface of therotating screen. The screen is rotated at a speed WASTEWATERCONCENTRATION METHOD to achieve a desired centrifugal force. Effluentpasses through 9 l m 13 Drawing 5- the screen to an outlet and theremaining concentrate passes 52 u.s.c| 210/78, w A certain splashes210571210330 the inner surface of the screen, and is received by abacksplash 511 int. Cl 130m 21/26 and may be and The Screen is so Fleldof Search 210/78, the form of a Screen cage having a p'uramy 377, 380screen panels for facilitating replacement of damaged screens orchanging of screen type or mesh size. Cleaning means is [56] ReferencesCited provided for directing a cleaning fluid periodically at the UNITEDSTATES PATENTS screen. The methods disclosed involve the manner in whichthe influent, effluent, concentrate and backsplash are hangrzz ig died,and the manner in which the influent is screened to 946476 lllglo warn210/380 X achieve a fluid concentrate which is pumpable to other treat-3 51 1373 5/1970 ggg gi 209/234 ment equipment for ultimate disposal.Additionally, a

sequence of influent feed and screen cleaning is described. PrimaryExaminer-Jim L. De Cesare A!mrney- Lyon & Lyon Pmmmd Dec. 14, 1971 6Sheets-Sh 2 mmmm Pmmmmd Um. 14, 1971 6 Sheets-Sheet 5 Patemed cc,14,1971- 6 Sheets-Sheet New Dec. 14, 1971 6 Sheets-Sheet 6 WASTEWATERCONCENTRATION METHOD CROSS REFERENCE TO RELATED APPLICATIONS Theconcepts disclosed herein are related to those disclosed in copendingapplication Ser. No. 640,241, filed May 22, 1967, entitled ScreeningApparatus Employing Rotating Cylindrical Screen and Stationary FeedMeans," now US. Pat. No. 3,239,008 and U.S. Pat. No. 3,5ll,373, both ofwhich are assigned to the assignee of the present application and thedisclosures of which are incorporated herein by reference. Briefly, saidapplication Ser. No. 640,24l disclosed apparatus involving a rotatingsubstantially cylindrical screen in combination with a stationarydistribution means for screening an influent. The screen anddistribution means may be used in combination with a downstream planarvibratory separator for further screening of the concentrate from therotating screen. Said US. Pat. No. 3,511,373 disclosed apparatus similarto that in said application and is directed to means for facilitatingcleaning of said rotating screen. Reference is also made to relatedapplications, filed concurrently herewith, Ser. No. 42,098, entitledUp-Flow Separator, filed in the name of Theodore R. Westfall; Ser. No.42,165, entitled "Improved Wastewater Concentration, tiled in the nameof Walter J. Talley, Jr.; and Ser. No. 42,099, entitled ImprovedRotating Screen Separator," filed in the name of Philip H. Mook. Theseapplications contain a similar disclosure to that set forth herein, butinclude claims directed to various of the structural and operationalfeatures disclosed herein.

BACKGROUND OF THE INVENTION This invention relates to the screening of aliquid-solids influent to achieve a desired separation ofliquids andsolids, and more particularly to screening of storm water, sewage orstorm water overflow from combined sewer systems.

Although the present inventive concepts are useful in screening variousmaterials, they have particular application for water pollution controland, thus, will be described in this environment and particularly forfine-mesh screening for primary treatment of storm water overflow fromcombined sewer systems. As set forth in a research report on treatmentof storm water overflow entitled Rotary Vibratory Fine Screening ofCombined Sewer Overflows" prepared by Cornell, Howland, Hayes andMerryfield in connection with Department of the interior Contract14-12-128 and dated Mar. I970, the majority of the existing combinedsewers throughout the nation donot have adequate capacity during heavystorm periods to transport all waste and storm-caused combined flows toa treatment facility. The overflow is bypassed to a receiving stream,thus causing pollution in the nation's water courses.

As further described in said report, the Federal Water Pollution ControlAdministration published a report in 1967 reviewing the effects andmeans of correcting combined sewer overflows on a national basis. of the200 million people residing in the United States, approximately 125million are served by combined or separate sewer systems, and of the 125million, approximately 29 percent are served by combined sewers.Combined sewers are designed to receive all types of waste flows,including storm water, for ultimate treatment at a treatment facility.in determining the size of the combined sewer, it has been commonengineering practice to provide capacity for three to five times thedry-weather flow. During intensive storm periods, however, thestorm-caused combined flow may be two to 100 times the dry-weather flow,making overflow conditions unavoidable. To compound the problem, mosttreatment facilities are not designed to handle the hydraulic load ofthe combined sewer and, therefore, are required to bypass a portion ofthe storm-caused combined flow to protect the treatment facility andtreatment process from damage. The nation s treatment facilities bypassflows an estimated 350 hours during the year, or about four percent ofthe total operation time. The pollutional impact of the stormcausedcombined overflow of the waters of the nation has been estimated asequivalent to as much as 160 percent of the strength of the domesticsewage biochemical oxygen demand. This amount creates a major source ofpollution for the nations water courses. The Cornell et al. reportfurther describes certain tests, results and recommendations withrespect to the use of high-rate fine-mesh screens for primary treatmentof storm water overflow from combined sewer systems, the equipmentdescribed being similar to that disclosed in said application Ser. No.640,241 and US. Pat. No. 3,51 L373. The present inventive conceptsinvolve certain improvements thereover.

in light of the foregoing, it is a principal object of the presentinvention to provide improved screening equipment and methods.

A further object of this invention is to provide an improved screeningdevice employing a rotating screen and distribution means associatedtherewith.

Another object of this invention is to provide an improved screeningdevice employing a rotating screen wherein an improved combination ofcentrifugal force and rate of flow of an influent is provided forachieving desired screening of said influent.

Other objects and features of the present invention will become apparentthrough a consideration of the following description and attacheddrawings.

SUMMARY OF THE lNVENTlON There is disclosed herein a screeningapparatus, such as for use in screening of storm water overflows fromsewer systems, comprising a substantially cylindrical rotary screendevice disposed for rotation within a housing, feed means for directingan influent toward the inner surface of the screen, and outlet means forreceiving (a) the effluent which passes through the screen, (b) theconcentrate which does not pass the screen, and (c) backsplash from thescreen.

The feed means includes an upwardly extending feedpipe, or the like, forsupplying the influent to the screen. The feed means may includeadjustable means for varying the rate of flow of influent, and deflectormeans may be provided for directing the flow of influent as a pluralityof substantially discrete inclined streams toward the inner surface ofthe screen.

The rotary screen is in the form of a substantially cylindrical cage andincludes a plurality of screen panels, which may be removed for repair,cleaning or replacement with different mesh screens or different screencloth. The speed of rotation of the screen is selected to provide adesired centrifugal force, or g-loading of influent on the screen, theg-loading being a function of the radius of the screen and the square ofthe r.p.m. thereof. The velocity of flow of influent onto the screen isselected within a preferable range below which suitable impingement doesnot occur, and above which excessive splashback and possible screendamage may occur. A typical flow velocity is in a range approximately 13to 15 feet per second, and exemplary preferred screen speeds areapproximately 65 r.p.m. for a 60inch diameter screen and 88 r.p.m. for a36-inch diameter screen, it being; appreciated that other suitable flowvelocities, screen speeds, diameters, and the like may be employedwithout departing from the present concepts.

The influent preferably is screened to achieve a relatively fluidconcentrate, as distinguished from a dry concentrate, so that the samemay be readily transported or pumped for further treatment or disposal.

A screen cleaning apparatus is provided for spraying cleaning fluidthrough the screen at desired intervals. in the screening of aninfluent, it is preferable to cyclically (a) feed the influent for apredetermined period of time, (b) terminate the feed, (0) spray thescreen with a cleaning fluid for a shorter predetermined period, and (d)return the feed of influent. An exemplary cycle includes feedinginfluent for 4% minutes and cleaning the screen for A minute, includinga cleaning spray from outside to inside of the screen for a few secondsand then inside to outside of the screen for a few seconds.

Although a complete screening apparatus and method involving a number ofnovel concepts and structures are disclosed herein, this application isparticularly directed to the concept of efficient screening of wastewater and the like by a rotating screening device wherein a suitablecombination of influent flow rate and centrifugal force is provided toachieve a desired split in the resulting efiluent and concentrate;whereas said other applications filed concurrently herewith are directedto other novel features disclosed herein.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a cross-sectionalelevational view of a preferred screening apparatus;

FIG. 2 is a top plan view of the apparatus of FIG. 1;

FIG. 3 is a cross-sectional view of the apparatus taken along a line3--3 of FIG. 1;

FIGS. 4A and 4B are cross-sectional views illustrating an adjustableinfluent plate of the apparatus of FIG. 1;

FIG. 5 is a perspective view of a distribution dome of the apparatus ofFIG. 1;

FIG. 6A is a top view and FIGS. 68 and 6C are fragmentarycross-sectional views of the distribution dome of FIG. 5;

FIG. 7 is a partial perspective view of a rotary screen cage of theapparatus of FIG. 1;

FIG. 8 is a partial top view of the screen of FIG. 7; and

FIGS. 9A and 9B are views illustrating the manner in which screen panelsare secured to the screen cage of FIG. 7.

DESCRIPTION OF PREFERRED EMBODIMENTS Turning now to the drawings, andparticularly to FIGS. 1 through 3, a rotary screening device isillustrated including an outer substantially cylindrical housing 10containing a rotary screen cage 11, an influent inlet feedpipe 12, aninfluent impingement plate or diverter 13, a drive assembly 14 for thescreen cage 11, an effluent outlet 15, a concentrate outlet 16, and abacksplash outlet 17. It should be noted at this point that FIG. 1 is anelevational'cross section view taken along a line 1-1 of FIG. 3;whereas, FIG. 3 is a cross-sectional plan view taken generally along aline 3-3 of FIG. 1.

As will be more fully explained subsequently, an influent, such as stormwater overflow having enormous amounts of water and relatively littlesolids, is fed to the feed pipe 12 and deflected outwardly by theimpingement plate 13 toward the inside of the rotating screen cage 11.The screen cage includes a plurality of screen panels, and the influentis screened resulting in a highly liquid effluent and a concentratewhich is substantially less liquid but flowable. The effluent isdischarged by outlet 15 and the concentrate is discharged by outlet 16.The screen cage 11 is rotated at a speed to provide a suitablecentrifugal force for the screening action, and the impingement plate 13is positioned to provide the desired flow rate of influent toward thescreen cage. A distribution dome 18 may be provided to direct theinfluent as a plurality of substantially discrete inclined flows towardthe inner surface of the screen cage. lnfluent which splashes back fromthe inner surface of the screen cage may be redirected to the cage formore complete screening, as by collecting the backsplash and recyclingthe same with incoming influent. The upflow of influent provided by thefeedpipe l2 simplifies the design and construction of the apparatus andinvolves less fluid head loss than encountered with a feed of influentto the screen cage from above the apparatus.

These screening concepts serve to reduce pollution caused, for example,by overflow of combined storm-sanitary sewage systems during periods ofheavy rainfall. As much as A; of the sewage solids settle to the bottomof large combined sewers and in periods of heavy rain, they flow intostreams, lakes,

overflow into receiving waters. As a result, combined treatment systemsoften loose more pollutants to their rivers and streams than they takeout in the treatment plant itself..

As will appear from the following description and drawings, the presentapparatus and concepts meet many storm-sanitary pollution controlrequirements for a compact, low-cost, highvolume, primary treatmentsystem. The present apparatus is capable of releaving a combined sewagesystem of its hydraulic overload during storm periods, while sending apollutant concentrate to the treatment plant. Exemplary apparatus isapproximately seven feet in diameter and six feet high and employsapproximately nine to l8 removable screen panels on a revolving screencage. A combination of high-velocity influent flow and centrifugal forcecan allow approximately to percent of a hydraulic flow of 3milliongallons per day to pass through the screens. The remaining concentratecontaining a high percentage, such as 99 percent, of the floatable andsettleable solids is discharged separately into the hydraulicallyrelieved sewage system.

Considering the construction of the apparatus in more detail, thehousing 10 includes a base 20, a substantially cylin drical upstandingwall 21, and covers 22 and 23 to provide a substantially closedcontainer. The screen drive assembly is secured to the top of theapparatus and includes a mounting plate 24 for supporting a motor, onlythe base 25 thereof being seen in the drawings, and a gearbox 26.Suitable support and spacing plates 27 through 29 are provided to whichan I-beam 30 with gussets 31 and 32 are secured to form a bearing mount.A pair of bearings 33 and 34 are secured to the bearing mount. A shaft35 is joumaled in the bearings 33 and 34 and has a drive pulley 36affixed at the upper end thereof. A pulley 37, as seen in FIG. 2, iscoupled with the output shaft of the gearbox 26, and the pulleys 36 and37 are coupled by means of V-belts 40 and 41. An idler 42 may beprovided to maintain proper belt tension. As will be apparent to thoseskilled in the art, the motor is coupled with the input shaft of thegearbox 26 in any suitable manner, as by V-belts, and drives the shaft35 through the gearbox, pulleys 37 and 36, and the V-betls 40 and 41. Acollar 43 is secured, as by welding, to the lower end of the shaft 35,and the screen cage 1 l is attached to this collar to enable the shaft35 to rotate the screen cage 1 1.

The wall 21 of the housing 10 extends upwardly as indicated at 44. Thecover 22 may bea lift-off cover, and includes windows 45 as seen in FIG.2 to enable observation of the interior of the apparatus. A removableaccess door cover 46 may be provided. The wall 21 of the housing 10 mayinclude a window 47 for observation of the interior of the apparatus.Suitable bracing is provided within the housing for structural purposesand for firmly supporting the various pipes. An angle bracket 48 andbraces 49, for example, are provided as illustrated in FIGS. 1 and 3.

The screen cage 11 will be described in more detail subsequently, butgenerally includes a cage formed of a lower angle ring 50, an upper barring 51, and a plurality of upstanding bars 52 extending between theangle ring 50 and bar ring 51 as best seen in FIGS. 7 and 8. Nine bars52 have been used for an exemplary cage approximately 36 inches indiameter. Support ribs 53 are connected between the various bars 52 anda central collar 54 which is secured to the collar 43 affixed to theshaft 35. Removable screen panels 56 having a frame and screeningmaterial of metal or cloth secured thereto are inserted between thevertical bars 52 and clamped thereto in a substantially sealedrelationship.

As noted earlier, an influent to be screened is supplied through theinfluent pipe 12 and directed upwardly toward the impingement plate 13.The plate deflects the flow outwardly toward the inner surface of thescreen panels 56 of the screen cage 11. The vertical position of theplate 13 is adjustable as will be explained subsequently so as tocontrol the rate of flow of influent. The distribution dome 18 as bestseen in FIGS. 1 and 5 is secured to the upper end of the pipe 12. Thisdome 18 includes a sleeve 60 which rest on a collar 61 affixed to thepipe 12, and a plurality of inclined plates 62 secured to the outersurface of the sleeve 60. A portion 63 of each plate may be bentupwardly as shown in FIG. 5, or separate spacers may form the portions63, and secured to the underside of the next succeeding plate was toform a rigid structure. The distribu tion dome 18 functions to directinfluent, which has been deflected by the impingement plate 113, intosubstantially inclined streams toward the inner surface of the screenpanels. An interior wall or divider 66 which is substantiallycylindrical is secured within the housing and extends almost up to thehorizontal surface of the flange of the angle ring 50. This dividerforms, in combination with the housing wall 21, an annular chamber 67for receiving effluent and directing the same to the effluent outlet 15.The effluent, as is known to those skilled in the art, is the materialwhich passes through the screen cage ill. The divider 66 also encloses aconcentrate chamber or bowl 68 which as an inclined bottom 69 fordirecting concentrate to the concentrate outlet 16.

A backsplash pan 71 is positioned within the chamber 68 and coupled witha support 72. The pipe 117 communicates with the interior of the pan 7E.The top of the pan 7] is approximately at the elevation of the bottom ofthe screen panels and the radius of the upper portion of the pan 71 isslightly smaller than the interior diameter of the screen cage 11 so asto receive influent which splashes back from the inner surface of thescreen cage 11 and screen panels 56. The radius of the pan 71 typicallymay be about two inches less than the radius of the screen cage 11.Concentrate flows through the gap between the interior of the cage andthe exterior of the pan 71 to the chamber 68.

The purpose of the backsplash pan 71 is to enable any influent whichsplashes from the screen cage 11 to be collected .for either recyclingwith incoming influent or sent to another separator device for screeningto ensure that the maximum desired split between effluent andconcentrate is achieved. A]- ternatively, other methods of collectingbacksplash may be provided, as for example a baffle below thedistribution dome 18 which catches or otherwise deflects the backsplashmaterial back toward the inner surface of the screen panels at the lowerportion of the screen cage 11. In a test with a 2200 gallon per minuteinfluent flow with no screen panels in the screen cage, it was foundthat 46 gallons of influent was collected in the chamber 68. lt isbelieved that this occurred because of backsplash from the screen cagebars 52. By recycling or further screening of this 46 gallons ofbacksplash in a normal operation with screens it has been computed thatthe split would be improved by two percent or better.

Turning again to the influent impingement plate 13, the same isadjustable up and down as noted earlier. The purpose of this adjustmentis to enable control of an orifice area 75 between the lower surface ofthe plate 13 and upper end of the sleeve 60 of the distribution dome 18,or upper end of the pipe 12 in the event the same extends above thesleeve 60. This allows control of the rate of flow of influent. Theplate 13 is secured to a rod 67 which extends upwardly through the shaft35 as seen in FIGS. 1 and 5a and 4b. The upper end of the rod 76 isthreaded into a threaded bushing 77 which is secured to the upper end ofthe shaft 35. The rod 76 thus may be adjusted up or down to vary theposition of the plate 13 with respect to the upper end of the sleeve 60,and may be locked in position by a locknut 78. With the constructionthus described, the plate 13 rotates with the screen cage ill, but maybe made stationary if desired by other suitable supporting structure.

The shape of the plate 12 may be other than flat, such as a segment ofasphere. However, it is desired that the flows ofinfluent toward theinner surface of the screen cage 11 be substantially perpendicular tothe inner surface of the screen panel 56 rather than significantlyinclined upwardly or downwardly as viewed in FlG. 1. If these flows aresharply inclined downwardly, the concentrate is excessively liquid; but,on the other hand, if the flows are precisely horizontal and thusperpendicular to the inner surface of the screen panels the flows do notfan out" sufficiently to give a wide sweeping flow onto the innersurface of the screen panels. Ac-

cordingly, it is desired that the flow of influent be almostperpendicular to the inner surface of the screen panels but at a slightdownward angle to obtain a divergent flow, or fan out of the flow, bythe time the influent hits the screen panels. Each flow of influentshould fan out anywhere from substantially the entire height of thescreen panels to approximately A: the height of the screen panels, orslightly less such as to provide an impingement area of influent ontothe screen panels about 6 inches high. Thus, it is desired that theflows fan out slightly, but still flow substantially horizontally fromthe orifice 75, the fanning out being accomplished by the distributiondome 18 into essentially discrete inclined streams. If only a portion ofthe height of the screen panels is swept by the influent flows, thepanels can be turned over end for end after a period of use to maximizescreen life.

As noted earlier, the majority of the existing combined sewersthroughout the nation do not have adequate capacity during heavy stormperiods to transport all waste and stormcaused combined flows to atreatment facility. The overflow is bypassed to a receiving stream, thuscausing pollution problems. One of the principal applications of thepresent invention is in screening enormous amounts of water with solids.such as storm overflow, to separate out the solids and provide arelatively fluid, as distinguished from dry, concentrate which can thenbe properly handled by a sewage treatment facility. The effluent can besuitably disposed of, as for example in a stream. In this manner, theenonnous amounts of water do not overtax the sewage treatment facility,while still enabling proper treatment of the maximum amounts of solidsfrom the overflow.

One of the principal objectives is to achieve a high split, thatis,,ratio of effluent (screened product) to concentrate (unscreenedproducts), while still obtaining a slightly fluid concentrate which canflow continuously from the apparatus and be supplied, as by pumping, tosubsequent primary treatment equipment without the problems involved inhandling a solids concentrate. A typical ratio is better than to fivewith the apparatus described herein and with a typical influent flow ofabout 1000 gallons per minute. A number of factors affect this split,one of the principal factors being the centrifugal force involved in thescreening operation, which varies as the square of the screen cage rpm.and as a direct function of the radius thereof. There is a band ofoptimum performance in terms of centrifugal force. It has been foundthat a centrifugal force of around 3 gs appears to be optimum inachieving the maximum split, although it is to be understood that theforce can be below or above this value somewhat. This approximate forceor band around 3 gs can be obtained with a screen cage speed ofapproximately 65 rpm. for a screen cage about 60 inches in diameter, andapproximately 88 rpm. for a screen cage about 36 inches in diameter.Substantially higher speeds do not improve the split. Additionally,other factors are important, in achieving the maximum split, and theseinclude the velocity of the feed of influent, such as approximately 13to 15 feet per second, which can be selected by varying the size of theorifice 75 through adjustment of the plate 13; directing of the flows ofinfluent substantially perpendicular to the inner surface of the screencage as noted earlier; recycling or other screening of backsplash fromthe screen cage; maintaining the screen panels clean; and theorientation of the screen cloth in the screen panels.

The centrifugal force is important in achieving the maximum force on thesolid and water particles for separation of the water from the solids,but must not be excessive because the solids will then tend to cling tothe screen and blind or clog the screen and, additionally, screen damagemy result from high forces. At the optimum force or band of force, thecon centrate flows by gravity down from the screen. The provision ofalmost perpendicular flows to the inner surface of the screen isimportant as noted earlier so as to achieve the max imum separation withthe minimum of backsplash or other deflection of influent from thescreen cage. As to flow velocity, if the same is too low, insufficientinfluent reaches thereto. The backsplash represents unscreened influent,much the screen cage. Channels for receiving the edges of the screenpanels 56 are provided by T-brackets 85 which are secured to the bars 52by threaded stubs 86 and 87 and respective wingnuts 88 and 89. Braces 91are secured between adjacent of which is believed to be deflected fromthe bars 52 of the 5 ribs 53, and a gasket 92 is affixed onto each brace91 to form a screen cage, and it is desired to recycle or otherwisefurther .seal with the top of each respective screen panel 56. The edgesscreen the backsplash to optimize the split. It will be apparent h fram3 0f he screen panel 56 which abut with the that the screen panels mustbe clean to achieve the be t bars 52 may have a bead of resilientmaterial 94 thereon to screening action, and a cycle of influent feedand spray cleanform a Seal between the r en panels and bars 52. Thepanel ing with a cleaning fluid is preferred as will be described sub-10 includes n a g r m a h Screen fabric may be secured sequently.thereto with an epoxy adhesive. Exemplary screen fabric is Theorientation of the screen cloth within the cage is impor- 165 TBCproviding 47 percent open area. Metal or synthetic tant from a wear-lifestandpoint. It is preferably that the fabrics can be used. Stainlesssteel fabric has been found suitascreen cloth be bias mounted to formthe screen panels 56 of 1 5 le. A removable cover 95 having a removablesection 96 may FIG. 7 rather than positioning the cloth such that thewires or be Provided r the p f the screen cage. thread of the screencloth run vertically and horizontally. The A Vent P p 97 y be Providedto the interior of the bias mounting disposes the wires or thread atsubstantially 45 housing 10 t0 h osphere. A plate 9 is attached to theangles resulting in better screen life because the screen wires Shaft 35above h cov r portions 22 and 23 of the housing. are stressed and flexedequally and uniformly by the flows of p ti of h sc ee ing apparatus ca ahigh r pressure influent. This longer life-allows the screen cage to runlonger area toward the periphery of the screen cage 11, and air is withless downtime therefore improving the efficiency of drawn in between theplate 98 and cover portions 22-23 and screening. Also the slope of theinclined plates 62 of the disvented by the vent pipe 97. This flow ofair past the plate 98 tribution dome l8 affects the height to which theflows impaids in maintaining the bearings 33 and 34 clean and moistureinge on the screen panels and, thus affects screen life. A six free. Theplate 98 prevents material from splashing onto the inch drop at the edgeof the plate where the radial length of bearings from the cover portion2243 where the shaft 35 exthe plate is 28 inches gives a slope of 21percent which has tends therethrough. been found suitable fora 60-inchdiameter cage. The following represent exemplary test data from theFurthermore, it is believed that the direction of rotation of screeningof influent by apparatus like that described and ilthe screen cage withrespect to the inclination of the plate 62 lustrated and employing whatis referred to as a 36 inch screen of the dome 18 may contribute toobtaining the most efficient cage, the actual inside diameter defined bythe inner surface screening operation. The direction of rotation of thescreen of the screen panels being approximately 30 inches. Table IA cage11 is preferably as indicated with respect to the screen sets forth dataobtained with a large orifice 75 opening; panel 56 illustrated in FIG. 5(counterclockwise) and as illuswhereas the data in table 13 involvesvariations in the orifice trated with respect to the screen cage in FIG.8. Referring 75 again to FIG. 5, the flows of influent leave theinclined plates 62 of the distribution dome 60 at substantially theangle of the plates 62 and are believed to aid in sweeping large solidparti- TABLE 1 cles from the rotating screen. Avera 8 Screen cleaning isachieved by means of supply pipes 80 and Feed percer lt Test approxconcen- 81 having respective groups of nozzles 82 and 83. The nozzlesNo. m Rpm tram Generalcommems 82 and 83 provide sprays of cleaning fluidthrough the screen 1,000 105 8.3 26 .p.m. splashback. panels. lt ISpreferred to feed influent for a per od of time, 1,000 0 2 3 Nogscreensynot rotating. such as 4% minutes to 5 minutes, stop the flow of influentand 1, 000 120 0. 8 No screens, rotating. spray the screen panels with acleaning fluid such as a hot i% 3 g water hypochlorite solution for /4to 1 minute, and then con- 1,000 93 1.0 Do. tinue to feed the influent.This operation continues cyclically, 78 $23 No slggens not mating. withthe cleaning period lasting, for example, one-half minute, 7g -g $11 rcr ns. 15 with a spray from the nozzles 82 for 10 seconds and then fromso 3, 22}: the nozzles 83 for 20 seconds. It is desired to clean thescreens 1,000 78 316 1,500 78 13.4 Do. before they get dirty WhICh canbe measured In terms of 650 7 g 2 Do degradation of the split, forexample, down to 90-to-l0. 000 0 0 5 23 35 P33 2-105 Turning again tothe screen cage, and particularly FIGS. 7 15 1,000 37 8,6 3 D8 through9, preferably the screen panels 56 are removable for a- AM W "-7. "Arepair or replacement, and can be readily locked in place in TABLE IBFeed, Average Test approx percent No. g.p.m R.p.m. Feed orificeconcentrate General comments 1, 000 90 4. 3 Screens as above, 40 (tJsec.feed velocity. 1, 000 90 2. 0 15 ftJsec. velocity, =3g 15.13. 1,000 902.3 1, 000 00 plus 1 turn 2. 2 1,000 90 minus 1 turn- 2.0 1, 000 90minus M turn 2. 0 1, 000 90 minus turn 2.0 1,000 90 plus $4, turn- 1.931,000 90 plus turn 1.76 1,000 90 3A plus 54 turn 1.67 1, 000 00 A plus1% turn.. 1.88 1,000 90 plus 1 turn 1.76 1,000 90 111115134 turn 2.001,000 00 plus turn 1.71 1,000 120 do 1.67 1,000 ..d0. 2.3 1,000 90 6'1.7

. .m. 8 91' 11 u on 1I,)0X(,)0 00 13 710 5.0 1,000 00 18/10' 7.7 Dirtyscreens.

1 Too short screen. 7

Tests I through .61 are on a clean water influent, and tests 33 and 34involve an approximately 250 part per million paper pulp solution. As isapparent from tables IA and 18, a split of 8.3 to 8.6 percent wasobtained in tests 1 through 15 on clean water; however, the feedimpingement velocity was well under 10 feet per second. Commencing withtest No. 16, changes were made in the impingement plate 13 adjustmentand thus represent performance in terms of concentrate split atdifferent orifice openings and r.p.m.s. The reference under the feedorifice column to +1 turn, 1 T, and so forth refer to turns of the rod76 which was threaded nine turns per inch. Test No. 25 represents thebest performance in terms of concentrate split. Test No. 30 indicatesthat no substantial improvement in split was gained by increasing ther.p.m. above 90 r.p.m. Ninety r.p.m. for this apparatus provides about3gs of centrifugal force which also has been found to be substantiallyoptimum for a 60 -inch separator unit operating at 65 r.p.m. Likewise nosubstantial improvement was found in test No. 3| at 60 r.p.m.

It should be noted that 124 r.p.m. gives over 6 gs and 60 r.p.m. givesless than 2 gs for the approximately 30 diameter screen involved.Although a useful split is obtained, more optimum operation occurs,consistent with maximum screen life and obtaining a slightly wetconcentrate, when the centrifugal force is nearer to 3 gs. However, itis intended herein by reference to approximately 3 gs centrifugal forceto refer to a band of centrifugal force around 3 gs such as l to 7 gs,but preferably closer to 3 gs.

The following table 1] includes data wherein the influent was rawsewage, and summarizes l4 test runs of the same unit. Initial testsutilizing a 165 fusion-bonded four mesh screen indicated a concentratesplit ranging from 6 to 8 percent. Later rungs with bias-mounted 165 TBCscreens indicated a substantial improvement in split as compared withthe fusion bonded 165/4. Test No. 6 is not believed to be representativebecause the influent was of unusual character. The 165 TBC screen panelsprovided the best performance at approximately 90 r.p.m. as can beseenfrom table II. it should be noted that the concentrate volume in bothtest Nos. 8 and 9 at the lower 62 r.p.m. increased substantially ascompared with the 90, r.p.m. cage speed. Also, test Nos. 10 and 11 at124 r.p.m. in dicate a wetter concentrate than at 90 r.p.m. The screenwas cleaned in a cyclic manner as previously described. It will be notedthat an increase in concentrate split was obtained by using the biasamount 165 TBC screen panels as compared to fusion bonded panels.Similar results in split have been ob tained with similar apparatushaving an approximately 60 inch diameter screen cage.

ll. A method of screening an influent containing substantial amounts ofliquid and relatively few solids, such as combined storm-sanitaryoverflow to prevent overload of sewer systems, with a rotarysubstantially cylindrical screening structure comprising feeding saidinfluent toward the inner surface of said screening structure to allowseparation of liquid from solids, and rotating said screening structureat a speed which 18 a function of the radius thereof to provide acentrifugal force in a range of approximately 1 to 5 gs on said influentbeing screened to separate said influent being screened into a liquideffluent which passes through said screening structure and asolids-containing concentrate and to allow said concentrate to flow fromthe inner surface of said screening structure.

2. A method as in claim ll wherein said influent is fed to the innersurface of said screen structure at a flow rate up to approximately 15feet per second.

3. A method as in claim 1 wherein said centrifugal force isapproximately 3 gs.

4. A method as in claim 3 wherein the radius of said screening structureis approximately l6 inches and said structure is rotated atapproximately 88 r.p.m. 5. A method as in claim 3 wherein the radius ofsaid screening structure is approximately 30 inches and said structureis rotated at approximately r.p.m. 6. A method as in claim 3 whereinsaid influent is fed to the inner surface of said screen structure at aflow rate up to approximately 15 feet per second. 7. A method ofscreening an influent containing substantial amounts of liquid andrelatively few solids, such as combined storm-sanitary overflow toprevent overload of sewer systems, with a rotary substantiallycylindrical screening structure comprising feeding said influent to theinner surface of said screening structure at a flow rate up toapproximately 15 feet per second to allow separation of liquid fromsolids, and rotating said screening structure at a speed which is afunction of the radius thereof to achieve a centrifugal force in therange of approximately 2 to 4 g: on said influent being screened toseparate said influent being screened into a liquid effluent whichpasses through said screening structure and a solids-containingconcentrate and to allow said concentrate to flow from the inner surfaceof said screening structure. 6. A method as in claim 7 wherein said flowrate of said influent and said speed of said screen- TABLE II ControlledFeed, teed Average approx. pening, percent Test No g.p.n1. R.p.m inchesconcentrate Type ,of screen 1 1, 000 83. 5 M 1 6.0 165/4tl1si0n bonded.2. 1, 000 83. 5 A 8. 0 165/4 bonded. 3. l, 000 103 6. 5 D0. 4, 1, 00010s 6.5 Do. 5. 1, 000 59 V 7. 5 D0. 6. 1, 000 as Q 2. 9 165 TBC(abnormal ieed 7- 1, 000 86 3.0 165 TBC (more normal eed). 8 l, 000 623. 8 165 TBC. 9 1, 000 62 3. 5 165 TBCr 10... 1, 000 124 3. l 165 T130.11 1, 000 124 2.9 165 T130. 12... 1, 000 90 V 2. 85 165 T130. 13... l,000 90 3. 25 5-165 TBC, panels, 4465/4 bonded panels. 14 1,000 90 5.0All panels 165/4 bonded.

The present embodiments of this invention are to be considered in allrespects as illustrative and not restrictive, the scope of the inventionbeing indicated by the appended claims rather than by the foregoingdescription, and all changes which come within the meaning and range ofequivalency of the claims therefore are intended to be embraced therein.

What is claimed is:

ing structure are selected within said respective ranges to provide asplit of better than approximately to 10 between efi'luent andconcentrate resulting from screening of said influent. 9. Amethod as inclaim 7 wherein said centrifugal force is approximately 3 g's.

m t: a

2. A method as in claim 1 wherein said influent is fed to the innersurface of said screen structure at a flow rate up to approximately 15feet per second.
 3. A method as in claim 1 wherein said centrifugalforce is approximately 3 g''s.
 4. A method as in claim 3 wherein theradius of said screening structure is approximately 16 inches and saidstructure is rotated at approximately 88 r.p.m.
 5. A method as in claim3 wherein the radius of said screening structure is approximately 30inches and said structure is rotated at approximately 65 r.p.m.
 6. Amethod as in claim 3 wherein said influent is fed to the inner surfaceof said screen structure at a flow rate up to approximately 15 feet persecond.
 7. A method of screening an influent containing substantialamounts of liquid and relatively few solids, such as combinedstorm-sanitary overflow to prevent overload of sewer systems, with arotary substantially cylindrical screening structure comprising feedingsaid influent to the inner surface of said screening structure at a flowrate up to approximately 15 feet per second to allow separation ofliquid from solids, and rotating said screening structure at a speedwhich is a function of the radius thereof to achieve a centrifugal forcein the range of approximately 2 to 4 g''s on said influent beingscreened to separate said influent being screened into a liquid effluentwhich passes through said screening structure and a solids-containingconcentrate and to allow said concentrate to flow from the inner surfaceof said screening structure.
 8. A method as in claim 7 wherein said flowrate of said influent and said speed of said screening structure areselected within said respective ranges to provide a split of better thanapproximately 90 to 10 between effluent and concentrate resulting fromscreening of said influent.
 9. A method as in claim 7 wherein saidcentrifugal force is approximately 3 g''s.